Over the past 10 years, a tremendous amount of data has accumulated, which demonstrates the role of glycolipid-reactive T cells in autoimmune disease, host defense and tumor development. T cells and NKT cells can respond to a broad pool of self and foreign antigens presented by CD1 molecules and can trigger killing of the antigen presenting cell, through cytotoxic T lymphocytes (CTLs), or recruit help (T helper cells) from the humoral immune system through production of soluble antibodies. Our lab is interested in the molecular mechanisms of lipid antigen recognition in cell-mediated immunity. Toward this goal, we determine the binding kinetics of various glycolipidreactive T cell receptor[unreadable]s (TCR[unreadable]s) with various CD1 antigen-presenting molecules by surface plasmon resonance studies (SPR). We will further correlate the obtained results with data obtained by measuring cytokine production upon T cell activation using T cell hybridomas. Ultimately we propose to determine the three-dimensional structure of CD1 antigen receptors in complex with different lipids and cognate T cell receptors (TCR[unreadable]s) by x-ray crystallography. We specifically address the following specific aims: 1) What are the biochemical and functional properties of human and mouse sulfatide-reactive NKT cells. We will determine the structure of sulfatide loaded human CD1a and mouse CD1d in complex with the respective TCR and characterize their binding kinetics by SPR. Comparisons of both complexes will provide insights into the similarities and disparieties of sulfatide recognition by the immune system and will shed light on the molecular mechanism of their activation. 2) We will structurally and functionally characterize differences in glycolipid recognition of Borrelia burgdorferi glycolipids by human and mouse NKT cells. 3) We will characterize binding of novel endogenous self-lipids to mouse CD1d and their recognition by NKT cells. Structural insights into the differences of self vs. microbial antigen presentation will help understand the role of microbial lipids and lipid-reactive T cells in host defense and autoimmune diseases.